SPG Object 261

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SPG Object 261
SPG Object 261

Self-propelled artillery mount of increased power "Object 261"

The Object 261 self-propelled artillery mount was developed at the design bureaus of the Chelyabinsk and Leningrad Kirov plants on the basis of the IS-7 experimental heavy tank. A modified ship diesel M-50 of high power was used as the engine. The lightly armored open wheelhouse housed a powerful 152-mm M-31 cannon, it was developed at the Design Bureau of the Perm plant No. 172 on the basis of the ballistics of the Br-2 cannon and was unified in a number of parts with the M-51 tank gun. The M-31 cannon was tested in October 1948. The project of the self-propelled artillery unit "Object 261" was developed in 1947.

Despite the failures with the previous self-propelled guns of increased power, the idea of putting super-powerful guns on self-propelled chassis did not leave the Soviet leadership even after the war.

The deeply modernized gun Br-2 received a new name - M-31. The modernization was carried out so deeply that little remained of the Br-2. Design work was carried out by the design bureau of plant No. 172. The main differences from the Br-2 were as follows: not a piston, but a horizontal wedge semiautomatic breech, a powerful slotted muzzle brake, which absorbed up to 70% of the recoil energy. The barrel of the gun was equipped with a massive breech to obtain the required weight of the recoil parts and to better balance the swinging part. The loading of the new gun was separate-case. The sending of the projectile was carried out using the rammer spring, which is automatically cocked upon rollback. The barrel bore blowing mechanism also worked automatically. It used compressed air from a separate cylinder. The recoil brake was made hydraulic, and the recuperator was pneumatic. Two rollback brake cylinders and two recoil cylinders were made rigidly connected to the barrel. Thus, due to the breech and recoil devices, the weight of the recoiling parts was significantly increased, which, together with the muzzle brake, gave a very small recoil for a gun with such ballistics (520 mm versus 1400 mm for the Br-2). The lifting and turning mechanisms of the gun were of a sector type with a worm self-braking link. The lifting mechanism had only a manual drive, since the requirement for an electric drive of the GAU was removed (a rather strange decision). The M-31 gun had a TP-47A sight for direct fire and a ZIS-3 sight for firing from closed positions. And finally, this gun was originally designed to be unified with the 152-mm M-51 tank gun, which had the same ballistic data.


The technical design of the M-31 gun, finalized and agreed with the Chelyabinsk plant, was sent for consideration and conclusion to the Artkom GAU at the end of 1947. The gun got just unique data. The firing range of the gun was almost 28 km (27800 meters) with an initial projectile speed of 880 m / s. However, the project of the self-propelled object 715 presented by the Chelyabinsk plant (later it became known as the IS-7 tank) was not approved, and it was returned to the plant for revision. In this regard, a radical revision of the entire layout of the gun was required, although when considering its technical design, significant comments did not arise.


Taking into account the first design experience, plant No. 172 was asked to agree on the design of the cannon with the design of the ACS based on the IS-7 tank (ob. 261), developed in Leningrad. This work was carried out by plant number 172, and on August 23, 1948, a revised design of the M-31 cannon was submitted for consideration by the GAU, in relation to the combat compartment of the ACS based on the IS-7. However, the project of this ACS (object 261) was also rejected. And again, NTK BT offered the Leningrad Kirov Plant to redo the layout of the entire self-propelled gun. Plant No. 172 again had to change the design of the cannon, or rather, its machine, since the swinging parts of the cannon have never changed. By the way, from this we can conclude how close the IS-7 was to the conveyor. Our designers did not develop an ACS on the basis of an experienced unapproved chassis. But let's touch a little on the project of the ACS itself as a whole, as I said above, it was supposed to be produced on the IS-7 chassis. It was supposed to be equipped with a modified ship diesel engine M-50 with a capacity of 1050 hp. (the same as on the IS-7). With such a motor, according to the calculations of the designers, the ACS was supposed to reach a speed of 55 km / h and had a cruising range of 300 km. As for the ammunition load, it has not yet been approved in the ACS project.


The gun and the crew were to be located in a lightly armored open wheelhouse. This suggests that the designers of this SPG did not plan for its participation in tank duels. But the base of the ACS was left well armored (apparently for the sake of unification with the IS-7) and it had armor from 215 to 150 mm (by the way, in what place on the ACS they planned to install armor plates of 215 mm it remained unclear to me, after all, on the IS- 7, only the turret had such a thickness of armor, but the SPG does not have it, but these are the official performance characteristics of the self-propelled gun)

As it is not difficult to guess, with such data, the self-propelled gun turned out to be more than heavy. Its mass should have been somewhere in the region of 68 tons. True, her donor, the IS-7, had approximately the same weight.

Also, it should be noted that the alteration of the chassis of the IS-7 tank was supposed to be quite deep. The ACS was supposed to be based on, as it were, backwards to the front of the deployed chassis. That is, the engine, and the drive wheel, had to be located in front of the self-propelled gun.

This self-propelled gun also did not see the light of day, even in an experimental version. After the decision was made to abandon the production of the IS-7, this project, of course, was also rejected.



Base - tank IS-7

Combat weight, t - about 68

Body length, mm - 7380

Width, mm - 3400

Clearance, mm - 450

Average specific ground pressure, kg / cm2 - 0.9


Type - diesel M-50T

Developer - Design Bureau of Plant No. 800

Manufacturer - plant No. 800 ("Zvezda")

Maximum power, h.p. - 1050

Maximum speed, km / h - 55

Cruising in store, km - 300

Overcoming obstacles:

Ascent, hail - 30

Brod, m - 1, 5

Reservation, mm - 150-215

Radio station - 10PK-26

Artillery armament - one 152 mm M-31 howitzer cannon

Developer - Design Bureau of Plant No. 172

Manufacturer - plant No. 172

Maximum firing range, km - 27800

The initial speed of a high-explosive fragmentation projectile, m / s - 880

Sight - TP-47A, ZIS-3

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